Lasing improvement of Yb: phosphate glass with GeO2 modification

A series of GeO2 modified Yb: phosphate glasses were studied, covering thermal, optical, and fluorescence properties relevant to lasing performance. The host phosphate glass modified by introducing a second glass former, GeO2, was shown to have improved thermal stability, i.e., higher glass transition temperature (Tg) and lower coefficient of thermal expansion (CTE). Enlargement of Yb3+ 2F7/2: Stark splitting, broadening of effective fluorescence linewidth (∆λeff) and longer fluorescent lifetime (τf) were also achieved at the same time, whereas emission cross section (σemi) of the modified glasses were kept nearly constant. Selective laser experiments were performed; while the baseline host phosphate glass failed in lasing, a GeO2-modified phosphate glass was able to deliver 370 mW laser output at 1063 nm. Significant improvement of the lasing performance was further demonstrated using a newly designed GeO2-modified Yb: phosphate glass based on our study, which demonstrated 724 mW laser output at 1063 nm. The overall results from our study showed that germanium-phosphate glass system can be developed as a promising material for high energy, large scale Yb3+ laser.